SiC (silicon carbide) is expected as a material for a next-generation semiconductor device. SiC have excellent physical properties. In comparison with Si (silicon), a band gap is three times, breakdown electric field strength is approximately ten times, and thermal conductivity is approximately three times. A low-loss semiconductor device which can operate at a high temperature can be realized by using such properties.
However, for example, an interface state density between a semiconductor and an insulating layer is increased in the case where a metal insulator semiconductor field effect transistor (MISFET) is formed by using SiC in comparison with the case where Si is used. Therefore, there is a problem that mobility of electrical charges is decreased, and on-resistance of the MISFET is increased.
For example, there is a method in which N (nitrogen) or P (phosphorus) are introduced into the interface between SiC and an insulating layer to terminate an interface state. When this method is used, N (nitrogen) or P (phosphorus) functions as an n-type dopant, and a threshold voltage of an n-channel type MISFET may be decreased.
In order not to cause malfunction of a SiC-MOSFET, a threshold voltage at least equal to or greater than 3 V may be required at an operation temperature (for example, 200° C.), and preferably the threshold voltage is equal to or greater than 5 V. In case termination by nitrogen or phosphorus being applied, the threshold voltage may falls down to around 1 V.